Light-emitting device

ABSTRACT

A light-emitting device comprises a first light-emitting semiconductor stack comprising a first active layer; a second light-emitting semiconductor stack below the first light-emitting semiconductor stack, wherein the second light-emitting semiconductor stack comprises a second active layer; a wavelength filter between the first light-emitting semiconductor stack and the second light-emitting semiconductor stack; a protecting layer between the wavelength filter and the second light-emitting semiconductor stack; and wherein the first light-emitting semiconductor stack further comprises a first semiconductor layer and a second semiconductor layer sandwiching the first active layer, the second light-emitting semiconductor stack further comprises a third semiconductor layer and a fourth semiconductor layer sandwiching the second active layer, wherein the second semiconductor layer has a first band gap, the third semiconductor layer has a second band gap, and the protecting layer has a third band gap between the first band gap and the second band gap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication, Ser. No. 14/550,016, entitled “A METHOD FOR MAKINGLIGHT-EMITTING DEVICE”, filed on Nov. 21, 2014. The disclosures of allreferences cited herein are incorporated by reference.

TECHNICAL FIELD

The disclosure relates to a light-emitting device, and more particularlyto a light-emitting device comprising a protecting layer.

DESCRIPTION OF BACKGROUND ART

Light-emitting diodes (LEDs) are widely used as light sources insemiconductor devices. Compared to conventional incandescent light lampsor fluorescent light tubes, light-emitting diodes have advantages suchas lower power consumption and longer lifetime, and therefore theygradually replace the conventional light sources and are applied tovarious fields such as traffic lights, back light modules, streetlighting, and medical equipment.

FIG. 14 schematically shows a conventional light-emitting devicecomprising an LED 51, a submount 52 having an electrical circuit 54, anda solder 56 electrically connecting the electrical circuit 54 of thesubmount 52 to the LED 51, wherein the LED 51 comprises a substrate 53,and a wire 58 for electrically connecting an electrode 55 of the LED 51to the electrical circuit 54 of the submount 52.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a light-emitting device, comprising afirst light-emitting semiconductor stack comprising a first activelayer; a second light-emitting semiconductor stack below the firstlight-emitting semiconductor stack, wherein the second light-emittingsemiconductor stack comprises a second active layer; a wavelength filterbetween the first light-emitting semiconductor stack and the secondlight-emitting semiconductor stack; a protecting layer between thewavelength filter and the second light-emitting semiconductor stack;wherein the first active layer emits a first radiation of a firstdominant wavelength, and the second active layer emits a secondradiation of a second dominant wavelength longer than the first dominantwavelength; and wherein the first light-emitting semiconductor stackfurther comprises a first semiconductor layer and a second semiconductorlayer sandwiching the first active layer, the second light-emittingsemiconductor stack further comprises a third semiconductor layer and afourth semiconductor layer sandwiching the second active layer, whereinthe second semiconductor layer has a first band gap, the thirdsemiconductor layer has a second band gap, and the protecting layer hasa third band gap between the first band gap and the second band gap.

The present disclosure provides a light-emitting device, comprising afirst light-emitting semiconductor stack comprising a first activelayer; a second light-emitting semiconductor stack below the firstlight-emitting semiconductor stack, wherein the second light-emittingsemiconductor stack comprises a second active layer; a wavelength filterbetween the first light-emitting semiconductor stack and the secondlight-emitting semiconductor stack; an etching stop layer between thewavelength filter and the second light-emitting semiconductor stack,wherein the etching stop layer has a first transverse width; a firstcontact layer between the etching stop layer and the secondlight-emitting semiconductor stack, wherein the first contact layer hasa second transverse width; wherein the first active layer emits a firstradiation of a first dominant wavelength and the second active layeremits a second radiation of a second dominant wavelength longer than thefirst dominant wavelength; and wherein the second transverse width isgreater than the first transverse width.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the light-emitting device in accordance with oneof the embodiments of the present application;

FIG. 2 is a cross-sectional diagram along an A-A′ line in FIG. 1;

FIGS. 3 through 6 are cross-sectional views of a light-emitting deviceduring a manufacturing process in accordance with one of the embodimentsof the present application shown in FIG. 2;

FIG. 7 is a cross-sectional diagram along an A-A′ line in FIG. 1;

FIG. 8 is a cross-sectional view of a light-emitting device during amanufacturing process in accordance with one of the embodiments of thepresent application shown in FIG. 7;

FIG. 9 is a cross-sectional diagram along an A-A′ line in FIG. 1;

FIG. 10 is a cross-sectional view of a light-emitting device during amanufacturing process in accordance with one of the embodiments of thepresent application shown in FIG. 9;

FIG. 11 is a cross-sectional diagram along an A-A′ line in FIG. 1;

FIG. 12 is a cross-sectional view of a light-emitting device during amanufacturing process in accordance with one of the embodiments of thepresent application shown in FIG. 11;

FIG. 13 is a cross-sectional view of a light-emitting structure inaccordance with one of the embodiments of the present application; and

FIG. 14 shows a conventional light-emitting device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present application will be described indetail with reference to the accompanying drawings hereafter. Thefollowing embodiments are given by way of illustration to help thoseskilled in the art fully understand the spirit of the presentapplication. Hence, it should be noted that the present application isnot limited to the embodiments herein and can be realized by variousforms. Further, the drawings are not precise scale and components may beexaggerated in view of width, height, length, etc. Herein, the similaror identical reference numerals will denote the similar or identicalcomponents throughout the drawings.

In the present application, if not specifically mention, the generalexpression of AlGaAs means Al_(x)Ga_((1-x))As, wherein 0<x<1; thegeneral expression of AlInP means Al_(x)In_((1-x))P, wherein 0<x<1; thegeneral expression of AlGaInP means (Al_(y)Ga_((1-y)))In_(x)P_(1-x),wherein 0≦x≦1, 0≦y≦1, and x+y=1; and the general expression of InGaPmeans In_(x)Ga_(1-x)P, wherein 0<x<1. The content of the element can beadjusted for different purposes, such as matching the lattice constantof the growth substrate or reflecting a predetermined wavelength range.

FIG. 1 is a top view of a light-emitting device 1 in accordance with oneembodiment of the present application. FIG. 2 is a cross-sectionaldiagram along an A-A′ line in FIG. 1. As shown in FIG. 1 and FIG. 2, thelight-emitting device 1 comprises a first light-emitting semiconductorstack 10 and a second light-emitting semiconductor stack 20, a firstDistributed Bragg reflector 30 interposed between the firstlight-emitting semiconductor stack 10 and the second light-emittingsemiconductor stack 20, a first contact layer 40 interposed between thefirst Distributed Bragg reflector 30 and the second light-emittingsemiconductor stack 20, a second contact layer 50 below the secondlight-emitting semiconductor stack 20, a bonding layer 60 below thesecond contact layer 50, a permanent substrate 70 below the bondinglayer 60, a first electrode 80 above and electrically connected to thefirst contact layer 40, a second electrode 81 below and electricallyconnected to the permanent substrate 70, a third contact layer 90 abovethe first light-emitting semiconductor stack 10, and a third electrode82 above the third contact layer 90. The first Distributed Braggreflector 30, the first light-emitting semiconductor stack 10 and thesecond light-emitting semiconductor stack 20 are on the same side of thepermanent substrate 70. In one embodiment, the first light-emittingsemiconductor stack 10 and the second light-emitting semiconductor stack20 are epitaxially grown originally from a growth substrate, andpreferably, from the same growth substrate. Specifically, each layerbetween the second contact layer 50 (included) and the third contactlayer 90 (included) is formed by epitaxial growth. Preferably, the thirdcontact layer 90, the first Distributed Bragg reflector 30, the firstcontact layer 40, and the second contact layer 50 are substantiallylattice-matched to the growth substrate, and more preferably, the firstlight-emitting semiconductor stack 10, which is further to the permanentsubstrate 70 than the second light-emitting semiconductor stack 20, isalso lattice-matched to the growth substrate. In the embodiment of thegrowth substrate composed of GaAs, each of the layers between the secondcontact layer 50 (excluded) and the third contact layer 90 (included)comprises a material other than GaP. The method of performing epitaxialgrowth comprises, but is not limited to metal-organic chemical vapordeposition (MOCVD), hydride vapor phase epitaxial (HVPE) or liquid-phaseepitaxy (LPE).

FIGS. 3 through 6 are cross-sectional views of a light-emitting deviceduring a manufacturing process in accordance with one of the embodimentsof the present application shown in FIG. 1. As shown in FIG. 3, a methodfor making the light-emitting device comprises the steps of: providing agrowth substrate 100; forming the third contact layer 90 by epitaxialgrowth; forming the first light-emitting semiconductor stack 10 on thethird contact layer 90 by epitaxial growth; forming the firstDistributed Bragg reflector 30 on the first light-emitting semiconductorstack 10 by epitaxial growth; forming the first contact layer 40 on thefirst Distributed Bragg reflector 30 by epitaxial growth; forming thesecond light-emitting semiconductor stack 20 on the first contact layer40 by epitaxial growth; and forming the second contact layer 50 on thesecond light-emitting semiconductor stack 20 by epitaxial growth. Asshown in FIGS. 4 through 6, the method for making the light-emittingdevice further comprises steps of: connecting the second contact layer50 to a permanent substrate 70 by a bonding layer 60; removing thegrowth substrate 100 from the third contact layer 90; removing a part ofthe third contact layer 90, a part of the first light-emittingsemiconductor stack 10, an a part of the first Distributed Braggreflector 30 to expose a part of the first contact layer 40 bylithography and etching process; and forming the first electrode 80 onthe first contact layer 40, forming the second electrode 81 below thepermanent substrate 70, and forming the third electrode 82 on the thirdcontact layer 90 respectively. Each layer from the first light-emittingsemiconductor stack 10 to the second light-emitting semiconductor stack20 is formed by epitaxial growth and thus complicated connecting stepssuch as bonding steps between different light-emitting semiconductorstacks are avoided. Therefore, the method of the present applicationshortens the steps for making the light-emitting device. Besides,because the first Distributed Bragg reflector 30 and the secondlight-emitting semiconductor stack 20 can be directly formed on thefirst light-emitting semiconductor stack 10 by epitaxial growth, thefirst light-emitting semiconductor stack 10, the first Distributed Braggreflector 30 and the second light-emitting semiconductor stack 20 are onthe same side of the growth substrate 100. As a result, it isunnecessary to flip over the growing substrate 100 during epitaxialgrowth.

Referring to FIG. 2, in the present embodiment, the first light-emittingsemiconductor stack 10 comprises a first semiconductor layer 11, asecond semiconductor layer 12 and a first active layer 13 interposedbetween the first semiconductor layer 11 and the second semiconductorlayer 12, wherein the conductivity type, the electrical property, thepolarity, and/or the dopant of the first semiconductor layer 11 aredifferent from that of the second semiconductor layer 12. In one of thepresent embodiment, the first semiconductor layer 11 comprises an n-typesemiconductor for providing electrons. The second semiconductor layer 12comprises a p-type semiconductor for providing holes. The firstsemiconductor layer 11 and the second semiconductor layer 12 comprise aGroup III-V semiconductor material, such as AlInP, AlGaInP or AlGaAs.The n-type dopant can be Si or Te. The p type dopant can be C, Zn or Mg.In the present embodiment, the first semiconductor layer 11 and thesecond semiconductor layer 12 comprises AlInP. The first active layer 13emits a first radiation of a first dominant wavelength in a visiblewavelength range or invisible wavelength range. Preferably, the firstdominant wavelength is in the red range. More preferably, the, firstdominant wavelength is between 620 nm and 790 nm. The secondlight-emitting semiconductor stack 20 comprises a third semiconductorlayer 21, a fourth semiconductor layer 22 and a second active layer 23interposed between the third semiconductor layer 21 and the fourthsemiconductor layer 22, wherein the conductivity type, the electricalproperty, the polarity, and/or the dopant of the third semiconductorlayer 21 are different from that of the fourth semiconductor layer 22.Preferably, the third semiconductor layer 21 of the secondlight-emitting semiconductor stack 20, which is closer to the firstDistributed Bragg reflector 30 than the fourth semiconductor layer 22,is of the same conductivity type as the second semiconductor layer 12,which is closer to the first Distributed Bragg reflector 30 than thefirst semiconductor layer 11 of the first light-emitting semiconductorstack 10. In the present embodiment, the third semiconductor layer 21comprises a p-type semiconductor for providing holes. The fourthsemiconductor layer 22 comprises an n-type semiconductor for providingelectrons. The third semiconductor layer 21 and the fourth semiconductorlayer 22 comprise a Group III-V semiconductor material, such as AlGaAs,AlInP or AlGaInP. The n-type dopant can be Si or Te. The p type dopantcan be C, Zn or Mg. In the present embodiment, the third semiconductorlayer 21 comprises carbon-doped AlGaAs, and the fourth semiconductorlayer 22 comprises Tellurium-doped AlGaAs. Besides, the thirdsemiconductor layer 21 and the fourth semiconductor layer 22 can be asingle layer and each has a thickness less than 500 nm, and preferably,between 300 and 500 nm both inclusive. Furthermore, the thirdsemiconductor layer 21 and the fourth semiconductor layer 22 each has adoping concentration between 5*10¹⁷/cm³ and 5*10¹⁸/cm³ both inclusive.The second active layer 23 emits a second radiation of a second dominantwavelength longer than the first dominant wavelength. Preferably, thesecond dominant wavelength is in an invisible wavelength range. Morepreferably, the second dominant wavelength is between 790 nm and 1500 nmboth inclusive. The structure of the first active layer 13 and thesecond active layer 23 each can be single heterostructure (SH), doubleheterostructure (DH), double-side double heterostructure (DDH) ormulti-quantum well (MQW), wherein the first dominant wavelength and thesecond dominant wavelength can be changed by adjusting the compositionand the thickness of the first active layer 13 or the second activelayer 23. The material of the first active layer 13 and the secondactive layer 23 comprises a Group III-V semiconductor material, forexample, the first active layer 12 comprises alternate well layerscomposed of InGaP and barrier layers composed of AlGaInP, and the secondactive layer 23 comprises alternate well layers composed of InGaAs andbarrier layers composed of AlGaAsP. In the present embodiment, the thirdcontact layer 90 has a light exit surface (not labeled) opposite to thepermanent substrate 70, and the light emitted from the first activelayer 13 and the light emitted from the second active layer 23 areescaped from the light-emitting device 1 mainly through the light exitsurface of the third contact layer 90. The first active layer 13 iscloser to the light exit surface of the third contact layer 90 than tothe second active layer 23 for preventing the first radiation emitted bythe first active layer 13 from being absorbed by the second active layer23.

Referring to FIG. 2, in the present embodiments, the first DistributedBragg reflector 30 is electrically conductive and has a higherreflectivity to the first dominant wavelength than to the seconddominant wavelength. That is to say, the Distributed Bragg reflector 30reflects more first radiation than the second radiation. Specifically,the difference between the reflectivity of the Distributed Braggreflector 30 to the first dominant wavelength and the reflectivity tothe second dominant wavelength is greater than 30%, and preferablygreater than 40%, and more preferably greater than 50%. Specifically,the Distributed Bragg reflector 30 has a transmittance to the seconddominant wavelength greater than 30%, and preferably greater than 50%,and more preferably greater than 80%. To be more specific, a wavelengthrange with reflectivity greater than 50% of the first Distributed Braggreflector 30 does not overlap the second dominant wavelength, andpreferably, a wavelength range with reflectivity greater than 80% of thefirst Distributed Bragg reflector 30 does not overlap the seconddominant wavelength, and more preferably, a wavelength range withreflectivity greater than 90% of the first Distributed Bragg reflector30 does not overlap the second dominant wavelength, wherein thewavelength range can be changed by adjusting the material or thethickness of the first semiconductor layers, the thickness of the secondsemiconductor layers, or the pair number of the first semiconductorlayers and the second semiconductor layers, wherein a firstsemiconductor layer and a second semiconductor layer are considered as apair. The first active layer 13 is closer to the first Distributed Braggreflector 30 than to the first contact layer 40. The first DistributedBragg reflector 30, the first contact layer 40, the second semiconductorlayer 12, and the third semiconductor layer 21 are of the sameconductivity type. In the present embodiment, the first DistributedBragg reflector 30 is a p-type semiconductor. Besides, the transversewidth of the first Distributed Bragg reflector 30 is less than thetransverse width of the second light-emitting semiconductor stack 20,and less than the transverse width of the first contact layer 40. Thefirst Distributed Bragg reflector 30 comprises alternate firstsemiconductor layers and second semiconductor layers, wherein therefractive index and the thickness of the first semiconductor layers aredifferent from that of the second semiconductor layers. The material ofthe first Distributed Bragg reflector 30 comprises a Group III-Vsemiconductor material, such as Al_(x)Ga_((1-x))As/Al_(y)Ga_((1-y))As(wherein x is different from y) or AlInP/AlGaInP, wherein the content ofAl and Ga and the content of Al and In can be adjusted for reflecting apredetermined wavelength range.

Referring to FIG. 2, in the present embodiments, the secondlight-emitting semiconductor stack 20 is closer to the first contactlayer 40 than to the first Distributed Bragg reflector 30. The firstelectrode 80 is electrically commonly connected to the firstlight-emitting semiconductor stack 10 and the second light-emittingsemiconductor stack 20 through the first contact layer 40 for formingohmic contacts between the first electrode 80 and the firstlight-emitting semiconductor stack 10 and between the first electrode 80and the second light-emitting semiconductor stack 20. The first contactlayer 40, the second semiconductor layer 12, and the third semiconductorlayer 21 are of the same conductivity type. In the present embodiment,the first contact layer 40 is a p-type semiconductor. The thickness ofthe first contact layer 40 is less than 1 um and preferably, less than500 nm, and more preferably, between 50 and 100 nm both inclusive forreducing light absorption by the first contact layer 40. The dopingconcentration of the first contact layer 40 is greater than 10¹⁹/cm³,and preferably, between 1*10¹⁹/cm³ and 5*10¹⁹/cm³ both inclusive. Thematerial of the first contact layer 40 comprises a Group III-Vsemiconductor material, such as GaAs, AlGaAs, InGaP or AlGaInP. Thedopant of the first contact layer 40 can be Zn or Carbon. In the presentembodiment, the material of the first contact layer 40 comprisescarbon-doped GaAs.

Referring to FIG. 2, in the present embodiments, the second contactlayer 50 and the third contact layer 90 are of the same conductivitytype, wherein the second electrode 81 is electrically connected to thesecond light-emitting semiconductor stack 20 through the second contactlayer 50 for achieving ohmic behavior between the second electrode 81and the second light-emitting semiconductor stack 20, and wherein thethird electrode 82 is electrically connected to the first light-emittingsemiconductor stack 10 through the third contact layer 90 for achievingohmic behavior between the third electrode 82 and the firstlight-emitting semiconductor stack 10. In the present embodiment, thesecond contact layer 50 and the third contact layer 90 are n-typesemiconductors. The thickness of the second contact layer 50 is lessthan 1 um, and preferably, less than 500 nm, and more preferably,between 50 and 100 nm both inclusive for reducing light absorption bythe second contact layer 50. The doping concentration of the secondcontact layer 50 is greater than 10¹⁸/cm³, and preferably, between5*10¹⁸/cm³ and 5*10¹⁹/cm³ both inclusive. The material of the secondcontact layer 50 comprises a Group III-V semiconductor material, such asGaAs, AlGaAs, InGaP or AlGaInP. The thickness of the third contact layer90 is less than 1 um, and preferably, less than 500 nm, and morepreferably, between 50 and 100 nm both inclusive for reducing lightabsorption by the third contact layer 90. The doping concentration ofthe third contact layer 90 is greater than 10¹⁹/cm³, and preferablybetween 5*10¹⁸/cm³ and 5*10¹⁹/cm³ both inclusive. The material of thethird contact layer 90 comprises a Group III-V semiconductor material,such as GaAs, AlGaAs, InGaP or AlGaInP. In the present embodiment, thematerial of the third contact layer 90 comprises silicon-doped GaAs.

Referring to FIG. 2, in the present embodiments, the bonding layer 60 isfor connecting the second contact layer 50 to the permanent substrate70. The bonding layer 60 is electrically conductive and comprises ametal material selected from the group consisting of In, Au, Sn, Pb,InAu, SnAu, and the alloys thereof.

Referring to FIG. 2, in the present embodiments, the permanent substrate70 is electrically conductive for conducting a current flowing betweenthe first electrode 80 and the second electrode 81 and conducting acurrent flowing between the second electrode 81 and the third electrode82. The permanent substrate 70 has a thickness thick enough forsupporting the layers or structures thereon. The material of thepermanent substrate 70 comprises a conductive material or preferably atransparent conductive material. The conductive material comprises Si,Cu, Al, Mo, Sn, Zn, Cd, Ni, Co, diamond like carbon (DLC), graphite,carbon fiber, metal matrix composite (MMC) or ceramic matrix composite(CMC).

Referring to FIG. 2, the first electrode 80, the second electrode 81,and the third electrode 82 are for electrically connected to an externalpower source for independently driving the first light-emittingsemiconductor stack 10 and the second light-emitting semiconductor stack20. In one embodiment, under an driving condition of the first electrode80 being positive and the second electrode 81 and the third electrode 82being negative, the first light-emitting semiconductor stack 10 isforward biased by the first electrode 80 and the third electrode 82;meanwhile, the second light-emitting semiconductor stack 20 is forwardbiased by the first electrode 80 and the second electrode 81. Therefore,the first electrode 80 and the first contact layer 40 are electricallycommon to the first light-emitting semiconductor stack 10 and the secondlight-emitting semiconductor stack 20. Besides, the first light-emittingsemiconductor stack 10 and the second light-emitting semiconductor stack20 can be operated independently, therefore the applied voltages acrossthe first light-emitting semiconductor stack 10 and the secondlight-emitting semiconductor stack 20 can be different. The material ofthe first electrode 80, second electrode 81 and the third electrode 82comprises transparent conductive material or metal material, wherein thetransparent conductive material comprises transparent conductive oxide,and wherein the metal material includes Cu, Sn, Au, Ni, Pt, Al, Ti, Cr,Pb, Cu—Sn, Cu—Zn, Cu—Cd, Sn—Pb—Sb, Sn—Pb—Zn, Ni—Sn, Ni—Co, Au alloy,Au—Cu—Ni—Au or combinations thereof.

FIG. 7 shows another embodiment of a light-emitting device 2 inaccordance with the present disclosure. The light-emitting device 2comprises substantially the same structure as shown in FIG. 2, andfurther comprises a protecting layer 110 between the first DistributedBragg reflector 30 and the first contact layer 40. Preferably, theprotecting layer 110 is also lattice-matched to the growth substrate. Inthe embodiment of the growth substrate composed of GaAs, each of thelayers between the second contact layer 50 (excluded) and the thirdcontact layer 90 (included) comprises a material other than GaP. Themethod for making the light-emitting device 2 comprises the stepssubstantially the same as the method for making the light-emittingdevice 1, and further comprises a step of forming the protecting layer110 on the first Distributed Bragg reflector 30 by epitaxial growthbefore the step of forming the first contact layer 40 as shown in FIG.8. In the present embodiment, the second semiconductor layer 12 has afirst band gap and the third semiconductor layer 21 has a second bandgap. The protecting layer 110 has a third band gap between the firstband gap and the second band gap. The protecting layer 110 iselectrically conductive and is of the same conductivity type as thefirst contact layer 40. In the present embodiment, the protecting layer110 is a p-type semiconductor. The protecting layer 110 has a thicknessless than 1 um, and preferably, less than 500 nm, and more preferably,between 50 nm and 100 nm both inclusive. Preferably, the protectinglayer 110 has a doping concentration between 1*10¹⁷/cm³ and 1*10¹⁹/cm³both inclusive. The material of the protecting layer 110 comprises aGroup III-V semiconductor material, such as AlInP, AlGaInP, or InGaP.Because the first dominant wavelength of first active layer 21 and thesecond dominant wavelength of second active layer 23 are different, thematerial of the first light-emitting semiconductor stack 10 and thesecond light-emitting semiconductor stack 20 are different. Therefore,the epitaxial system for growing the first light-emitting semiconductorstack 10 is different from that of the second light-emittingsemiconductor stack 20. During the process of changing the epitaxialsystem chamber, the protecting layer 110 is for preventing the layersbetween the growth substrate 100 and first Distributed Bragg reflector30 from oxidization and deterioration. Specifically, the protectinglayer 110 comprises Al and has an Al composition ratio less than the Alcomposition ratio of the layer which the protecting layer 110 isdirectly grown on. In another embodiment, the protecting layer 110 isdirectly grown on the Distributed Bragg reflector 30 comprising Al, andthe protecting layer 110 comprises InGaP and is substantially devoid ofAl. Furthermore, the following epitaxial layers such as the firstcontact layer 40 which is directly formed on the protecting layer 110 byepitaxial growth is substantially lattice-matched to the protectinglayer 110.

FIG. 9 shows another embodiment of a light-emitting device 3 inaccordance with the present disclosure. The light-emitting device 3comprises substantially the same structure as shown in FIG. 7, andfurther comprises a first current spreading layer 120 between theprotecting layer 110 and the first contact layer 40, a second currentspreading layer 130 between the third contact layer 90 and the firstlight-emitting semiconductor stack 10. Preferably, the first currentspreading layer 120 and the second current spreading layer 130 are alsolattice-matched to the growth substrate. In the embodiment of the growthsubstrate composed of GaAs, each of the layers between the secondcontact layer 50 (excluded) and the third contact layer 90 (included)comprises a material other than GaP. Furthermore, in the presentembodiment, the third semiconductor layer 21 and the fourthsemiconductor layer 22 of the second light-emitting semiconductor stack20 each has a thickness between 500 nm and 5000 nm so as to act as acladding layer and a current spreading layer for the secondlight-emitting semiconductor stack 20 at the same time. The method formaking the light-emitting device 3 comprises the steps substantially thesame as the method for making the light-emitting device 2, and furthercomprises the steps of forming the second current spreading layer 130 onthe third contact layer 90 by epitaxial growth before the step offorming the first light-emitting semiconductor stack 10; and forming thefirst current spreading layer 120 on the protecting layer 110 byepitaxial growth before the step of forming the first contact layer 40as shown in FIG. 10. The first current spreading layer 120 is of thesame conductivity type as the first contact layer 40. In the presentembodiment, the first current spreading layer 120 is a p-typesemiconductor. The first current spreading layer 120 comprises a GroupIII-V semiconductor material, such as AlGaAs. In the present embodiment,the material of the first current spreading layer 120 comprisescarbon-doped AlGaAs. The second current spreading layer 130 comprises aGroup III-V semiconductor material, such as AlGaInP. The first currentspreading layer 120 and the second current spreading layer 130 are forspreading the current more uniformly through the first light-emittingsemiconductor stack 10. The third semiconductor layer 21 and the fourthsemiconductor layer 22 are for spreading the current more uniformlythrough the second light-emitting semiconductor stack 20. In one of theembodiments, the light-emitting device comprises one of the first andthe second current spreading layers instead of comprising both of them.

FIG. 11 shows another embodiment of a light-emitting device 4 inaccordance with the present disclosure. The light-emitting device 4comprises substantially the same structure as the light-emitting device3 described in FIG. 9 and the description thereof, and thelight-emitting device 4 optionally comprises an etching stop layer 140between the first contact layer 40 and the first current spreading layer120. Preferably, the etching stop layer 140 is also lattice-matched tothe growth substrate. In the embodiment of the growth substrate composedof GaAs, each of the layers between the second contact layer 50(excluded) and the third contact layer 90 (included) comprises amaterial other than GaP. The method for making the light-emitting devicecomprises the steps substantially the same as the method for making thelight-emitting device 3 as described in FIG. 9 and the descriptionthereof, and optionally comprises a step of forming the etching stoplayer 140 on the first current spreading layer 120 by epitaxial growthbefore the step of forming the first contact layer 40 as shown in FIG.12. The etching stop layer 140 is electrically conductive and is of thesame conductivity type as the first contact layer 40. In the presentembodiment, the etching stop layer 140 is a p-type semiconductor. Theetching stop layer 140 has a thickness between 50 nm and 100 nm bothinclusive, and has a doping concentration between 1*10¹⁷/cm³ and1*10¹⁹/cm³ both inclusive. The material of the etching stop layer 140comprises a Group III-V semiconductor material, such as AlInP, AlGaInP,or InGaP. The material of the etching stop layer 140 may be the same ordifferent from the protecting layer 110. The etching stop layer 140 isfor preventing from over-etching the first contact layer 40 during thestep of removing a part of the third contact layer 90, a part of thesecond current spreading layer 130, a part of the first light-emittingsemiconductor stack 10, a part of the first Distributed Bragg reflector30, a part of the protecting layer 110 and a part of the first currentspreading layer 120 to expose a part of the first contact layer 40.

In one embodiment, the first dominant wavelength of the first radiationand the second dominant wavelength of the second radiation are bothgreater than 600 nm. Preferably, the first radiation is red light, andthe second radiation is infra-red light. Specifically, the firstdominant wavelength of the first radiation is between 650 nm and 670 nm,and the second dominant wavelength of the second radiation is between795 nm and 815 nm or between 930 nm and 950 nm. More specifically, thefirst dominant wavelength of the first radiation is about 660 nm. Thesecond dominant wavelength of the second radiation is about 805 nm orabout 940 nm. The first Distributed Bragg reflector 30 reflects thefirst radiation and is substantially transparent to the secondradiation. The material of the first Distributed Bragg reflector 30comprises Al_(x)Ga_((1-x))As/Al_(y)Ga_((1-y))As orAlInP/Al_(z)In_((1-z))GaP, wherein x is between 0.7 and 1 bothinclusive, y is between 0.4 and 0.6 both inclusive, and preferably, isbetween 0.3 and 0.5, and z is between 5 and 10 both inclusive forreflecting the first radiation. The first active layer 13 and the secondactive layer 23 may operate independently. Specifically, the firstactive layer 13 is operated by controlling the first electrode 80 andthe third electrode 82. The second active layer 23 is operated bycontrolling the first electrode 80 and the second electrode 81. Thelight-emitting device is a monolithic die comprising multiplelight-emitting semiconductors with different wavelengths used formultiple functions. As a result, a monolithic die comprising multiplelight-emitting diodes emitting different dominant wavelengths in asingle package is achieved, and therefore the volume of thelight-emitting device is significantly reduced. Furthermore, because thelight-emitting device is a monolithical single chip featured with dualdominant wavelengths while independently driving the first active layer13 and the second active layer 23, the light-emitting device of thepresent embodiment may be applicable in biomedical field as wearabledevices such as pulse oximeters for monitoring blood oxygen saturation(SpO2) and detecting hemoglobin by alternately or periodically drivingthe first light-emitting semiconductor stack 10 and the secondlight-emitting semiconductor stack 20.

Referring to FIG. 11, the light-emitting device 4 further comprises asecond Distributed Bragg reflector 150 between the second contact layer50 and the fourth semiconductor layer 22. Preferably, the secondDistributed Bragg reflector 150 is also lattice-matched to the growthsubstrate. Referring to FIG. 12, the method for making thelight-emitting device 4 of FIG. 11 further comprises a step of formingthe second Distributed Bragg reflector 150 on the fourth semiconductorlayer 22 by epitaxial growth before the step of forming the secondcontact layer 50. The second Distributed Bragg reflector 150 is forreflecting the second radiation. The transverse width of the secondDistributed Bragg reflector 150 is greater than the transverse width ofthe first Distributed Bragg reflector 30, and is substantially the sameas the transverse width of the second light-emitting semiconductor stack20. The second Distributed Bragg reflector 150 comprises alternate thirdsemiconductor layers and fourth semiconductor layers, wherein therefractive index and the thickness of the third semiconductor layers aredifferent from that of the fourth semiconductor layers. The material ofthe second Distributed Bragg reflector 150 comprises a Group III-Vsemiconductor material, such as Al_(x)Ga_((1-x))As/Al_(y)Ga_((1-y))As(wherein x is different from y), AlAs/GaAs, AlInP/InGaP orAl_(u)In_((1-u-v))Ga_(v)P/Al_(r)In_((1-r-s))Ga_(s)P (wherein u isdifferent from r). The second Distributed Bragg reflector reflectsradiation in a wavelength range overlapping the second dominantwavelength, and the wavelength range can be changed by adjusting thematerial, the thickness of the third semiconductor layers, the thicknessof the fourth semiconductor layers and the pair number of the thirdsemiconductor layers and the fourth semiconductor layers, wherein athird semiconductor layer and a fourth semiconductor layer areconsidered as a pair. The second Distributed Bragg reflector 150 can bealso applied to the foregoing embodiment depicted in FIG. 2 to FIG. 10.

Referring to FIG. 11, in one of the embodiments, the light-emittingdevice 4 optionally comprises a buffer layer 160 between the fourthsemiconductor layer 22 and the second contact layer 50. In oneembodiment, the buffer layer 160 is between the second Distributed Braggreflector 150 and the second contact layer 50. The method for making thelight-emitting device 4 further comprises a step of forming the bufferlayer 160 on the second Distributed Bragg reflector 150 by epitaxialgrowth before the step of forming the second contact layer 50. The bandgap of the buffer layer 160 is between the band gap of the fourthsemiconductor layer 22 and the band gap of the second contact layer 50.The lattice constant of the buffer layer 160 is between the latticeconstant of the fourth semiconductor layer 22 and the lattice constantof the second contact layer 50. The buffer layer 160 has a thicknessbetween 10 nm and 500 nm both inclusive, and has a doping concentrationbetween 1*10¹⁷/cm³ and 1*10¹⁹/cm³ both inclusive. The material of thebuffer layer 160 comprises a Group III-V semiconductor material, such asInGaP or AlGaInP. In the present embodiment, the material of the bufferlayer 160 comprises silicon-doped InGaP. The buffer layer 160 can bealso applied to the foregoing embodiment depicted in FIG. 2 to FIG. 10.

Referring to FIG. 11, the light-emitting device 4 optionally comprisesan intermediate layer 170 disposed between the second semiconductorlayer 12 and the first Distributed Bragg reflector 30. If the materialof the second semiconductor layer 12 and the material of the firstDistributed Bragg reflector 30 are different from the material of theprotecting layer 110, the intermediate layer 170 comprises an elementhaving a composition ratio transiting from the side near the secondsemiconductor layer 12 to the side near the protecting layer 110, andthus the intermediate layer 170 comprises the same element as in thematerial of the protecting layer 110 and as in the material of thesecond semiconductor layer 12. For example, if the material of thesecond semiconductor layer 12 comprises AlInP, the material of the firstDistributed Bragg reflector 30 comprisesAl_(x)Ga_((1-x))As/Al_(y)Ga_((1-y))As (wherein x is different from y),and the material of the protecting layer 110 comprises InGaP, theintermediate layer 170 comprising AlGaInP is interposed between thesecond semiconductor layer 12 and the first Distributed Bragg reflector30. Preferably, the material of the intermediate layer 170 has a bandgap between the band gap of the second semiconductor layer 12 and theband gap of the protecting layer 110, and more preferably, theintermediate layer 170 has a lattice constant substantially the same asthat of the second semiconductor layer 12 and that of the protectinglayer 110. The method for making the light-emitting device optionallycomprises a step of forming the intermediate layer 170 on the firstlight-emitting semiconductor stack 10 before the step of forming thefirst Distributed Bragg reflector 30. Preferably, the intermediate layer170, the protecting layer 110, the first Distributed Bragg reflector 30and the first contact layer 40 have the same conductivity type. Theintermediate layer 170 has a thickness between 0 nm and 30 nm. Theintermediate layer 170 is for transiting the material of the firstlight-emitting semiconductor stack 10 to another material, such as ofthe protecting layer 110, and is advantageous for reducing forward bias(V_(f)) of the light-emitting device 4. Specifically, in one embodimentof the present disclosure, the compositions of the intermediate layer170 is gradually changed and the lattice constant of the intermediatelayer 170 is also gradually changed from the side connected to thesecond semiconductor layer 12 to the side connected to first DistributedBragg reflector 30 accordingly such that the intermediate layer 170 issubstantially lattice-matched to both the second semiconductor layer 12and the first Distributed Bragg reflector 30 at the interfacesrespectively. In one embodiment, the intermediate layer 170 comprises amaterial of AlGaInP of which the Al content is gradually decreased andthe Ga content is gradually increased at a direction from the secondsemiconductor layer 12 toward the first Distributed Bragg reflector 30.The intermediate layer 170 can be also applied to the foregoingembodiment depicted in FIG. 7 to FIG. 10.

The light-emitting devices as mentioned above are able to combine withother downstream structures to form a light-emitting module. As shown inFIG. 13, the light-emitting module comprises a submount 151 comprisingmultiple separated electrical connectors 152; a solder 153 on thesubmount 151, wherein the solder 153 is used for affixing thelight-emitting device of the present application to the submount 151,and thus the solder 153 renders the second electrode 81 of thelight-emitting device electrically connected to one of the electricalconnectors 152 of the submount 151. The first electrode 80 and the thirdelectrode 82 are electrically connected to the other two electricalconnectors 152 by any methods such as wire bonding.

The foregoing description of preferred and other embodiments in thepresent disclosure is not intended to limit or restrict the scope orapplicability of the inventive concepts conceived by the Applicant. Inexchange for disclosing the inventive concepts contained herein, theApplicant desires all patent rights afforded by the appended claims.Therefore, it is intended that the appended claims include allmodifications and alterations to the full extent that they come withinthe scope of the following claims or the equivalents thereof.

What is claimed is:
 1. A light-emitting device, comprising: a firstlight-emitting semiconductor stack comprising a first active layer; asecond light-emitting semiconductor stack below the first light-emittingsemiconductor stack, wherein the second light-emitting semiconductorstack comprises a second active layer; a wavelength filter between thefirst light-emitting semiconductor stack and the second light-emittingsemiconductor stack; a protecting layer between the wavelength filterand the second light-emitting semiconductor stack; wherein the firstactive layer emits a first radiation of a first dominant wavelength, andthe second active layer emits a second radiation of a second dominantwavelength longer than the first dominant wavelength; and wherein thefirst light-emitting semiconductor stack further comprises a firstsemiconductor layer and a second semiconductor layer sandwiching thefirst active layer, the second light-emitting semiconductor stackfurther comprises a third semiconductor layer and a fourth semiconductorlayer sandwiching the second active layer, wherein the secondsemiconductor layer has a first band gap, the third semiconductor layerhas a second band gap, and the protecting layer has a third band gapbetween the first band gap and the second band gap.
 2. Thelight-emitting device according to claim 1, further comprising a firstcontact layer on the first light-emitting semiconductor stack, whereinthe first contact layer and the wavelength filter are of the sameconductivity type.
 3. The light-emitting device according to claim 2,further comprising an etching stop layer between the first contact layerand the protecting layer.
 4. The light-emitting device according toclaim 3, wherein the etching stop layer has a thickness between 50 nmand 100 nm both inclusive.
 5. The light-emitting device according toclaim 3, wherein the etching stop layer and the first contact layer areof the same conductivity type.
 6. The light-emitting device according toclaim 1, wherein the protecting layer has a thickness less than 1 um. 7.The light-emitting device according to claim 6, wherein the protectinglayer has a doping concentration between 1×10¹⁷/cm³ and 1×10¹⁹/cm³. 8.The light-emitting device according to claim 1, wherein the thirdsemiconductor layer and the second semiconductor layer are of the sameconductivity type.
 9. The light-emitting device according to claim 1,further comprising a first current spreading layer between theprotecting layer and the second light-emitting semiconductor stack. 10.The light-emitting device according to claim 9, further comprising anetching stop layer between the first current spreading layer and thesecond light-emitting semiconductor stack.
 11. The light-emitting deviceaccording to claim 1, further comprising an etching stop layer betweenthe protecting layer and the second light-emitting semiconductor stack.12. The light-emitting device according to claim 1, wherein thewavelength filter has a higher reflectivity to the first dominantwavelength than that to the second dominant wavelength.
 13. Thelight-emitting device according to claim 1, wherein the protecting layerhas a thickness between 50 nm and 100 nm both inclusive.
 14. Thelight-emitting device according to claim 1, wherein the protecting layerhas a doping concentration between 1×10¹⁷/cm³ and 1×10¹⁹/cm³ bothinclusive.
 15. The light-emitting device according to claim 1, whereinthe protecting layer comprises InGaP and is substantially devoid of Al.16. A light-emitting device, comprising: a first light-emittingsemiconductor stack comprising a first active layer; a secondlight-emitting semiconductor stack below the first light-emittingsemiconductor stack, wherein the second light-emitting semiconductorstack comprises a second active layer; a wavelength filter between thefirst light-emitting semiconductor stack and the second light-emittingsemiconductor stack; an etching stop layer between the wavelength filterand the second light-emitting semiconductor stack, wherein the etchingstop layer has a first transverse width; a first contact layer betweenthe etching stop layer and the second light-emitting semiconductorstack, wherein the first contact layer has a second transverse width;wherein the first active layer emits a first radiation of a firstdominant wavelength and the second active layer emits a second radiationof a second dominant wavelength longer than the first dominantwavelength; and wherein the second transverse width is greater than thefirst transverse width.
 17. The light-emitting device according to claim16, wherein the etching stop layer has a thickness between 50 nm and 100nm both inclusive.
 18. The light-emitting device according to claim 16,wherein the etching stop layer and the first contact layer are of thesame conductivity type.
 19. The light-emitting device according to claim16, wherein the etching stop layer has a doping concentration between1×10¹⁷/cm³ and 1×10¹⁹/cm³ both inclusive.
 20. The light-emitting deviceaccording to claim 16, wherein the wavelength filter has a thirdtransverse width less than the second transverse width.